In producing jewels and gems from natural gemstones, or from glass or plastic, flat facets are commonly formed to render the gem aesthetically pleasing. The most popular way of forming flat facets is to mount a stone to a holder, which is termed a dop, of a faceting machine and then to work the surface of the stone with a rotatably driven lap wheel. Lap wheels are typically made of metal such as copper, brass, tin, lead or cast iron, to which an abrasive is added that actually works the stone. These abrasives must be fairly hard, certainly harder than the gemstone to be faceted. Diamond powders and carborundum are abrasives that are commonly employed in early, cutting stages of the faceting process.
In the process of forming facets a series of lap wheels are employed. Initially, a lap wheel having a rough abrasive surface is used to cut the facet. Again, diamond powders and carborundum are commonly used as the abrasive material embedded in the lap wheel working surface. In the cutting phase several laps are used with abrasive powders of increasingly smaller size. As the size of the abrasive decreases the term prepolishing is often used to signify a second phase of the faceting process wherein the facet surface is worked more finely. Again, the size of the abrasive of the lap wheels used continues to decrease until what is termed the polishing phase is entered. Polishing laps used in this final phase commonly employ fine diamond powders, cerium, alumina or other polishing agents.
Softer materials may be employed as the working agent in polishing softer stones such as quartz and tourmalines. Harder stones, as previously stated, require harder abrasive agents such as diamond powders. The size of the abrasive powders or particles decrease from some 60 microns all the way down in some cases to 1/2 micron or even smaller in average diameter. This is roughly equivalent to a 400 to 50,000 grit range.
During the final polishing stage the faceter devotes a substantial amount of effort in an attempt to achieve an extremely smooth, "optically" flat surface that is free of scratches or blemishes. To the artisan this can be a very time consuming, frustrating and sometimes fruitless effort due to the persistent presence of small surface scratches. Also, polishing lap wheels almost invariably produces a surface that is slightly canted from that produced by the prepolish laps. When this occurs it takes a very substantial time to produce the new plane throughout the entire surface area due to the only weakly abrasive nature of the polishing laps. Alternatively, substantial time is taken in attempts at reorientation.
The quest for perfecting a method of polishing flat facets has been ongoing for years. Many reasons have been hypothesized as to the causes of the difficulty in achieving optically flat, highly reflective and attractive facets. For example, it is frequently thought that polishing laps need to have their lapping surfaces scored to work efficiently. Scoring has been thought to be necessary to avoid a perfectly smooth working surface from which a polishing agent could easily be thrown. It has also been thought necessary to avoid the generation of large amounts of heat and creation of partial vacuums. Other faceters have attributed this problem to lap contamination and to problems of aggregation and flow.
Flat facets have also been polished with the use of polishing slurries applied to smooth lap wheels. Their use, however, has also failed to eliminate the just described problems. The perceived problems of aggregation and flow have persisted with this which has been attributable to the tendency for polishing agents to accumulate in front of the leading edge of the facet being polished. In attempts to remedy aggregation and flow problems with the use of slurry type polishing agents, the consistency of the polishing slurry has been reduced and the direction of lap movement across the facet has been changed.
Whether polishing is done with a polishing lap or with polishing slurries, the formation of smooth, highly polished and reflective flat facets has remained a very difficult task. For a more detailed description of these problems and of the techniques employed in attempting to overcome them, reference may be had to the book by Glenn Vargas titled Faceting for for Amateurs which is well known to hobbyists and to professional faceters alike.